In a semiconductor device, in many cases, a structure in which an n-type region having an n conductivity type and a p-type region having a p conductivity type are formed and an electrode is connected to the n-type region and the p-type region is adopted. With higher efficiency being achieved in recent years in an apparatus where a semiconductor device is included, a semiconductor device is also required to achieve higher efficiency. In order to achieve higher efficiency of a semiconductor device, the electrode above should be low not only in its own resistance (electrical resistance) but also in contact resistance with the n-type region and the p-type region above.
Meanwhile, in order to achieve a higher withstand voltage and lower loss of a semiconductor device and to enable use thereof in an environment at a high temperature, silicon carbide (SiC) has recently been adopted as a material for forming a semiconductor device. SiC is a wide-bandgap semiconductor greater in bandgap than silicon (Si) that has conventionally widely been used as a material for forming a semiconductor device. Therefore, by adopting SiC as a material for forming a semiconductor device, a higher withstand voltage, a lower ON resistance and the like of a semiconductor device can be achieved. In addition, a semiconductor device adopting SiC as a material is also advantageous in that lowering in characteristics when used in an environment at a high temperature is less likely than in a semiconductor device adopting Si as a material.
In adopting SiC as a material for a semiconductor device, however, it is difficult to avoid increase in Schottky barrier between a p-type region, an n-type region and an electrode as compared with an example where Si is adopted as a material for a semiconductor device. Consequently, a problem of difficulty in suppression of increase in contact resistance between a p-type region, an n-type region and an electrode has arisen.
In contrast, it has been known that contact resistance can be lowered by adopting Ni (nickel) as a material for an electrode in contact with an n-type SiC region containing an n-type impurity (an impurity having an n conductivity type) and adopting Ti (titanium)/Al (aluminum) or AlSi alloy as a material for an electrode in contact with a p-type SiC region containing a p-type impurity (an impurity having a p conductivity type) (see, for example, Satoshi TANIMOTO et al., “Practical Device-Directed Ohmic Contacts on 4H—SiC,” IEICE Transactions C, the Institute of Electronics, Information and Communication Engineers, April 2003, Vol. J86-C, No. 4, pp. 359-367 (Non-Patent Document 1)).